Donna Hornburger has spent over four years trying to find out the truth surrounding her son's murder in October 2012.

"It just hurts to my heart, because that's my baby. My son."

Her son, 26-year-old Dominique Hornburger was sitting in his car with his girlfriend in a Westwood neighborhood when neighbors say a dark colored SUV pulled up. Someone got out of the SUV with a gun and opened fire.

Neighbors say they heard the shots.

"I heard gunshots, about five or six gunshots. I looked out the window."

"I saw a black SUV backing up the street and another lady run and got in the car."

The same day, homicide investigators developed a person of interest in Hornburger's murder. Two days later, Memphis Police charged 28-year-old Billy Aldridge with first-degree murder.

From the 911 call: "Somebody named Billy Aldridge shot my daughter's boyfriend outside his house. She was sitting outside with him."

The Hornburger family thought they were about to see justice in their son's murder case, but that changed when the district attorney's star witness changed her story in the courtroom.

Assistant Shelby County DA Greg Gilbert declined to go on camera for an interview, but he sent this statement:

In the case of Tennessee v. Aldridge, murder charges against the defendant had to be dismissed by the state — with the court's approval — when a witness who previously identified the defendant as the shooter testified in trial that she was no longer sure about that identification. The state was ethically bound to dismiss the case since it could no longer carry its burden of proof beyond a reasonable doubt.

Before the Hornburger family knew it, the murder charges against Aldridge were dismissed. They were left feeling helpless and still looking for justice in their son's case.

"We're not trying to be hard on nobody, we just want the truth," Dominique Hornburger's father said. "We are missing a link to our family now."

So far no one else has been arrested in Hornburger's murder, but his father has this message for his son's killer: "Just come forward and stand up to your crime, 'cause it's going to walk you down eventually. God ain't going to let you keep coming around doing people wrong."

If you know who killed Dominique Hornburger, call Memphis Police at 528-CASH. All calls are confidential.